Performance Analysis of Bio-Based Asphalt Mixtures Containing Lignin

Given the need to promote the circular economy and sustainability, one of the main current trends in road materials construction is to employ industrial residues and by-products deriving from renewable sources as extender, replacement or modifier of bitumen, obtaining the so-called "bio-binders". As regards, lignin can represent a potentially attractive solution, because it is the most abundant natural biopolymer, available in large quantity and characterized by certain chemical similarity with bitumen. In this context, this study focuses on the evaluation of two dense-grade asphalt mixtures for binder layer made with bio-binders containing two different lignins, as partial replacement of bitumen. A preliminary phase allowed to optimize lignin content (30% by bio-binder weight) based on empirical test (i.e. dynamic viscosity, penetration and softening point tests) with the aim of maximizing the bitumen replacement and at the same time obtaining two bio-binders having a consistency similar to a reference plain bitumen. In the second phase, two bio-based mixtures were produced by using the before-optimized bio-binders in different attempt contents. After mixing, specimens were produced by means of a gyratory compactor at set gyrations. Then, the two lignin-based asphalt mixtures were compared with the reference mixture in terms of workability, Indirect Tensile Strength (ITS) and water sensitivity. Despite the bio-based mixtures revealed a slightly penalized workability, overall results showed that they are characterized by fully comparable performances to the reference one, allowing a reduction of the effective bitumen content.